What To Do When Your Mac's Startup Disk is Almost Full

Don't panic. It happens to the best of us. Fortunately, you can likely fix it pretty easily. Years of use and abuse can leave a hard drive positively overflowing with random bits of stray data, read on to see how to find some free space when there doesn't seem to be any.

The Situation

If you haven't been there yet, you will be one day. One minute you're cruising along on your computer, importing those iPhone vacation photos or downloading your favorite band's new album, everything is just fine, the world is a friendly place.

Your startup disk is almost full, now what?

Then you see it. An unwelcome window that popped up out of no where to inform you that your startup disk is full. The world isn't friendly anymore. It's dark, crowded and claustrophobic. Your computer has reached the end of its limits and you don't have the cash to drop on a new one.

You used to treat your Mac like gold, but these days it's old, slow and full.

The cold hard truth is that you got sloppy. You used to treat your Mac like gold, but these days it's old, slow and full. You tell yourself that you need everything on it, but you know it's not true. Now you have no choice, you have to find ways to trim the fat. Where do you even start?

Before We Begin

Before we jump in and start cleaning up your startup drive, you're going to need a secondary storage drive. If you've got a decent drive lying in a closet or desk drawer, now is the time to grab it.

If you can afford it, grab a terabyte or two so you'll be set for a while.

If you don't, you'll need to buy one. If you can afford it, grab a terabyte or two so you'll be set for a while. The cost sucks, but the two alternatives are buying a new machine and deleting important data.

Step 1. Empty Your Trash

That error message that popped up on your screen is a 911 call. Your computer is crying out for help and you need some quick victories to bring it back from the brink.

The quickest, easiest way to get your morbidly obese startup drive to drop a few pounds is to empty the trash. Lazy users who rarely empty their trash can have gigs and gigs of useless clutter eating up their disk space.

Empty your trash for a quick storage grab.

If this describes you, go to Finder, hit Command-Shift-Delete and don't look back. Now make this a daily or at least weekly practice.

By now, many of you will have regained some precious storage space already. That was easy! Don't get cocky kid, you're not out of the dark yet.

Step 2. Clear Out Downloads and Desktop

The trash isn't the only place on your computer that tends to serve as a catchall for random bits of data. For some users, the Desktop and Downloads folders are gold mines of files that were added in a hurry and never organized.

If something has been there for longer than a week, it's time to either kill it or put it somewhere more intentional...

It's a good practice to think of both of these spots as transitional. If something has been there for longer than a week, it's time to either kill it or put it somewhere more intentional such as the Documents folder (or your external drive).

This is especially true of your Downloads folder, if you insist on using your Desktop for commonly used items, that's fine (it's an acceptable practice, it just means that we can't be friends) but at least make sure that your Downloads folder doesn't turn into a bottomless abyss.

Organize by Date Modified or Date Last Opened.

Keep your Downloads folder organized by Date Modified or Date Last Opened. If you haven't touched something in over thirty days, you probably don't need it as much as you thought you did when you downloaded it.

Step 3. Check Out Your Movies Folder

Everything up to this point was meant to be a quick fix, but now it's time to bring in the big guns. We need to free up ten, twenty or even hundreds of gigabytes of data as quickly as possible. If you want high impact, the best place to start is your Movies folder.

Go to Users/YourUserName and click on the Movies folder. Now hit Command-I and take a look at the top right of the window that pops up to see the amount of space this folder is eating up (it may take a minute or two to compute).

Video content is an unrivaled beast when it comes to storage and will fill up the largest of drives in no time.

When I do this to mine, I see that it's eating up 30GB of data. That's certainly no small chunk of ones and zeros, but don't be surprised if yours has that tripled. Video content is an unrivaled beast when it comes to storage and will fill up the largest of drives in no time.

The Movies folder is a prime place to target storage hogs.

Offload, But Be Careful

The first thing you need to do to help out your Movies folder is browse around and see what's in there so you can decide if anything can be trashed.

Lots of apps write to this folder and there could be significant clutter that you simply don't need. I've usually got a few old Screeny screencasts rolling around in here and maybe even some half-hearted iMovie projects that never went anywhere. Cut where you can and empty your trash again to get a sense of your progress.

If there is still a lot of data here that you can't bare to lose, it's time to offload anything not being regularly accessed to your external drive. Be careful though, lots of random video resources go into a video project (pictures, movies, clips, etc.). Hopefully, you've kept things nicely organized to keep projects portable. If not, you'll have some digging to do. Try tossing projects one at a time onto your drive and opening them on another machine to see if they're still working.

Step 4. Clean Up Music, Apps and Pictures

Music is another big offender so repeat the process above with your music folder. Go into Home/Music/iTunes/iTunes Music and see if you can find some old albums that you never listen to any more.

iTunes is another big offender for storage.

You'll need to create three mental categories: keep, toss and move to external drive. If your drive is still pretty full at this point, you're going to have to make some difficult cuts. If you have any music that was obtained through questionable means, now might be the good time to get back on the straight and narrow. There's always Spotify.

Mobile Apps

In your iTunes folder, you'll notice something that isn't music or even movies: Mobile Applications. If the size of this folder is over 10GB, I'll bet you have more than a few iOS apps that you use less than once a year or perhaps not at all. Many of the apps in here have been deleted from your phone or iPad, but still sit here eating up space on your Mac.

Many of the apps in here have been deleted from your phone or iPad, but still sit here eating up space on your Mac.

To find the big offenders, sort the Mobile Applications folder by size. My apps folder is over 11GB. I have over 500 apps, 19 of which are over 100MB a piece. You'll find that it's often the case that the largest apps are games. I download a million of these things but hardly ever find myself actually using them.

Sort by size to spot the largest apps.

If that description fits you too, crack open iTunes, click on "Apps" in the sidebar and start purging. You might want to kill some from your iOS devices while you're at it.

Where Else Do You Store Media?

Your Movies and iTunes folders are traditionally the two big places where media is held so this should theoretically take care of a sizable chunk of data. Another obvious spot is your Pictures folder, where iPhoto, Lightroom and Aperture data all tend to reside. Grab what you can and move it to your external drive.

Try to think of other folders or applications that hold big multimedia files (your Dropbox folder perhaps?) and see if you can trim them down.

Step 5. Kill Big Caches

Caches are temporary files meant to help speed up certain tasks. The problem is, cache files can become quite bloated over time. There are a lot of third party apps that charge you good money to help clean out the various caches on your system, but this isn't something beyond your reach.

Click on the Finder app, then hold down the Option key, and click "Go" in the menu bar. This will reveal the otherwise hidden user Library folder. Click on it and then find the "Caches" folder.

The Spotify cache is a beast.

Once you're in here, organize the folders by size like we did before and see if you can spot any really large folders. I found a Spotify cache (com.spotify.client) that totaled over 4.5GB! You can actually control the size of this file in the Preferences section of the Spotify client.

Generally, you can delete a cache like this and not have any issues at all, especially if it's something from a third party. To be sure, drag the cache to your Desktop and launch the app that uses it. If there are no issues, delete it!

Step 6. Time to Scan

By now, we've hit on the big, obvious places for lots of data to hide in the dark, gobbling up gigs like a hungry monster. At this point, there are a ton of different places that we could turn to for more trimming: the Applications folder, the Documents folder, Application Support, the list goes on.

Rather than manually check every space on your hard drive that could be problematic, it's time to pull in some help. There are quite a few great third party apps that will scan your hard drive and help you identify problematic areas. I personally recommend Disk Wave because it's completely free, super fast and extremely easy to use.

Disk Wave is an easy and free way to find out what's eating up your storage.

Once you download and launch the app, click on a drive and the app will start scanning it. From here you'll easily be able to identify large the largest folders on your machine. You could go the expensive and fancy data visualization route, but in all honesty this gets the job done great and won't cost you a dime.

Be Cautious

As you use an app like Disk Wave, be extremely careful. Just because a folder is eating up space doesn't mean that you can ditch it. Your machine is full of very important system files that you never want to touch.

The general rule here is, when in doubt, don't touch it! User data eats up tons of space on its own and its all generated by your actions so you should be able to roughly identify it based on app names and the like. Unless you're a real expert, clean up your mess and leave the operating system to its own devices. It's built to take care of itself.

How Did You Free Up Storage?

Hopefully, after walking through these steps, your startup disk has shed some serious pounds and will operate without unexpected warning messages. How much is enough? It's different for every unique user setup but as a general rule of thumb, keeping a free space buffer of around 15-20% of your total space should keep you in a good place. If you get below that, it's time to read this article again.

If you went through this process with the tutorial, leave a comment below and let us know about all the nooks and crannies where you found extra data hiding. How much storage were you able to free up?